Editing Danube Delta (section)

==Geography and geology==
[[File:Danube Delta evolution.gif|325px|thumb|left|Historical evolution of the Danube Delta (AD 1 – 2015)]]
The modern Danube Delta began to form after 4000 BC in a bay of the [[Black Sea]] when the sea rose to its present level. A sandy barrier blocked the Danube bay where the river initially built its delta. Upon filling the bay with [[sediment]], the delta advanced outside this barrier-blocked estuary after 3500 BC, building several successive lobes:<ref>{{cite journal |last1=Giosan |first1=Liviu |last2=Donnelly |first2=Jeffrey P. |last3=Constantinescu |first3=Stefan |last4=Filip |first4=Florin |last5=Ovejanu |first5=Ionut |last6=Vespremeanu-Stroe |first6=Alfred |last7=Vespremeanu |first7=Emil |last8=Duller |first8=Geoff A.T. |title=Young Danube delta documents stable Black Sea level since the middle Holocene: Morphodynamic, paleogeographic, and archaeological implications |journal=Geology |date=2006 |volume=34 |issue=9 |pages=757–760 |doi=10.1130/G22587.1 |bibcode=2006Geo....34..757G }}</ref> the St. George I (3500–1600 BC), the Sulina (1600–0 BC), the St. George II (0 BC–present) and the Chilia or Kilia (1600 AD–present). Several other internal lobes were constructed in the lakes and lagoons bordering the Danube Delta to the north (Chilia I and II) and toward the south (Dunavatz).<ref name=SR83012 /> Much of the [[alluvium]] in the delta and major expansion of its surface area in the form of lobes resulted from [[Erosion#Vegetative cover|soil erosion]] associated with human  clearing of forests in the Danube basin during the [[1st millennium|1st]] and 2nd millennium.<ref name=NYT91412>{{cite news |title=Comments From Ancient Deforestation, a Delta Is Born |url=http://green.blogs.nytimes.com/2012/09/14/from-ancient-deforestation-a-delta-is-born/ |access-date=17 September 2012 |newspaper=The New York Times |date=14 September 2012 |author=Rachel Newer |archive-date=1 May 2021 |archive-url=https://web.archive.org/web/20210501005406/https://green.blogs.nytimes.com/2012/09/14/from-ancient-deforestation-a-delta-is-born/ |url-status=live }}</ref><ref name=SR83012>{{cite journal |title=Early Anthropogenic Transformation of the Danube-Black Sea System |journal=Scientific Reports |date=30 August 2012 |volume=2 |issue=article number 582 |pages=582 |doi=10.1038/srep00582 |author1=Liviu Giosan |author2=Marco J. L. Coolen |author3=Jed O. Kaplan |author4=Stefan Constantinescu |author5=Florin Filip |author6=Mariana Filipova-Marinova |author7=Albert J. Kettner |author8=Nick Thom |quote=Sediment loads delivered by Danube River, the main tributary of the Black Sea, significantly increased as land use intensified in the last two millennia, which led to a rapid expansion of its delta. |pmid=22937219 |pmc=3430877 |bibcode=2012NatSR...2..582G }}</ref> Geologist [[Liviu Giosan]] told ''The New York Times'': 
<blockquote>Probably 40 percent of the Delta was built in the last 1000 years. Finding that was like a eureka moment.<ref name=NYT91412/></blockquote>

At present, the delta suffers from a large [[Sedimentary budget|sediment deficit]], after the construction of dams on the Danube and its tributaries in the later half of the 20th century. Construction of a dense network of shallow channels in the delta over the same period, a [[Sedimentation enhancing strategies|sedimentation enhancing strategy]], attenuated the deficit on the delta plain but increased erosion along the coast.<ref>{{cite journal |last1=Giosan |first1=Liviu |last2=Constantinescu |first2=Stefan |last3=Filip |first3=Florin |last4=Deng |first4=Bing |title=Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta |journal=Anthropocene |date=2013 |volume=1 |pages=35–45 |doi=10.1016/j.ancene.2013.09.001 |bibcode=2013Anthr...1...35G }}</ref><ref>{{cite web |title=Study Offers Economical Solutions for Maintaining Critical Delta Environments |url=http://www.whoi.edu/news-release/maintaining_deltas |website= |access-date=10 June 2021 }}</ref> The Danube Delta is a low [[alluvial plain]], mostly covered by [[wetlands]] and water. It consists of an intricate pattern of marshes, channels, streamlets and lakes. The average altitude is 0.52 m, with 20% of the territory below sea level, and more than half not exceeding one meter in altitude. Dunes on the most extensive [[strand plain]]s of the delta (Letea and Caraorman strand plains) stand higher (12.4 m and 7 m respectively). The largest lakes are lakes Dranov (21.7km<sup>2</sup>), Roșu (14.5km<sup>2</sup>) and Gorgova (13.8km<sup>2</sup>).
[[File:Dalmatian Pelican and Great Cormorant in danube delta.jpg|thumb|left|upright=1.35|Dalmatian pelican and great cormorant]]

=== Distributaries of the Danube ===

The [[Danube]] branches into three main [[Distributary|distributaries]] into the [[river delta|delta]], '''[[Chilia branch|Chilia]]''', '''[[Sulina branch|Sulina]]''', and '''[[Sfântu Gheorghe branch|Sfântul Gheorghe]] (Saint George)'''. The last two branches form the '''Tulcea''' channel, which continues as a single body for several kilometers after the separation from the Chilia. At the mouths of each channel [[Alluvion|gradual formation of new land]] takes place, as the delta continues to expand.

{| class="wikitable"
|+ Main distributaries of the Danube
|-
! Danube arm
!Length (km)
!Flow (m<sup>3</sup>/s)<br>(1921–1990)
|-
| ''' [[Chilia branch|Chilia]]'''
| 120
| 3800
|-
| ''' [[Sulina branch|Sulina]]'''
| 64
| 1250
|-
| ''' [[Sfântu Gheorghe branch|Sfântu Gheorghe]]'''
''' (Saint George)'''
| 70
| 1500
|-
|}
[[File:Danube Delta Distributary.jpg|thumb|Danube Delta Distributary in Kyslytsia village, Ukraine]]
'''[[Chilia branch|Chilia]]''', in the north, the longest, youngest, and most vigorous, with two secondary internal deltas and one microdelta in full process of formation at its mouth (to Ukraine).

'''[[Sulina branch|Sulina]]''', the central and thus the shortest arm, which consequently led to its extensive use for traffic and severe transformation. At its mouth is located the main port and a single settlement with urban characteristics of the Romanian part of the delta. Because of the [[alluvium]] deposited at its mouth, a channel gradually advancing into the sea (presently it has 10km) was built in order to protect navigation.

[[Sfântu Gheorghe branch|Sfântul Gheorghe]] ('''Saint George''' in English), in the south, is the oldest and most sparsely populated. Its [[alluvium]] has led to the creation, beginning in 1897, of the [[Sacalin Island]]s, which today measures 19km in length.
[[File:Danube delta chart.png|600px|thumb|center|Map created in 2010]]
[[File:Cañas (Phragmites australis), Delta del Danubio, Rumanía, 2016-05-28, DD 18.jpg|thumb|Danube Delta in Romania]]

=== Climate ===

The Danube Delta is considered to be among Romania's sunniest and driest regions.<ref>{{Cite web |last=Pont |first=Ulrich |date=2021 |title=Thermal Performance Analysis of Vernacular Houses in the Danube Delta |url=https://repositum.tuwien.at/bitstream/20.500.12708/18532/1/Ivan%20Adrian%20Bebe%20-%202021%20-%20Thermal%20performance%20analysis%20of%20vernacular%20houses%20in...pdf |access-date=24 November 2024 |website=Teschnische Universität Wien}}</ref> The mean annual temperature is 11°C (−1°C in January and 22&nbsp;°C in July), with mean precipitation between 400mm/year and 300mm/year. 

=== {{anchor|Main ecosytems}}Main ecosystems ===
[[File:Denube Delta Bank.JPG|thumb|Danube Delta in Romania]]
[[File:LeteaMill.jpg|thumb|upright|Danube Delta: old mill in [[Letea]]]]

The Danube Delta falls within the [[Pannonian steppe]] [[ecosystem]] of eastern Europe, with Mediterranean influences. As a young region in full process of consolidation, the Danube Delta represents a very favourable place for the development of highly diverse [[flora]] and [[fauna]], unique{{clarify|date=January 2016}} in Europe, with numerous rare species. It hosts 23 natural ecosystems, but due to the extent of [[wetlands]] an aquatic environment is prevalent; a terrestrial environment is also present on the higher grounds of the continental [[levees]], where [[xerophile]] ecosystems have developed. Between the aquatic and terrestrial environments is interposed a swampy, easily flooded strip of original flora and fauna, with means of adaptation to water or land, depending on the season or [[hydrological]] regime. At the contact between freshwater and sea water, some special physical, chemical and biological processes take place, which have led biologists to consider this area as a very different ecosystem called '''beforedelta'''. Musura Gulf, north of Sulina, and Saint George Gulf are considered the most representative of this type of ecosystem.

Situated on major migratory routes, and providing adequate conditions for nesting and hatching, the Danube Delta is a magnet for birds from six major [[ecoregions]] of the world, including the Mongolian, Arctic and Siberian. There are over 320 species of birds found in the delta during summer,<ref>{{Cite web |url=https://whc.unesco.org/en/list/588/video |title=Danube Delta – UNESCO World Heritage Centre<!-- Bot generated title --> |access-date=2019-12-26 |archive-date=2019-05-10 |archive-url=https://web.archive.org/web/20190510210914/http://whc.unesco.org/en/list/588/video |url-status=live }}</ref> of which 166 are hatching species and 159 are migratory. Over one million individual birds (including swans, ducks, and [[Eurasian coot|coots]]) winter here.

==== Ecosystem of running water ====

This comprises the arms of the Danube, and a series of its more important streamlets and channels. It is an environment rich in [[plankton]], worms, [[mollusc]]s, [[Larva|grub]]s, and [[sponge]]s, with numerous species of fish, such as the [[carp]], [[pike (disambiguation)#Fishes|pike]], [[pike perch]], [[sheat-fish]], and freshwater [[sturgeons]] ([[sterlet]], Vyza{{Typo help inline|reason=Vyza? Please give Latin name|date=February 2021}}  and Danube mackerel{{Typo help inline|reason=Suspicious vernacular name. Please give Latin name|date=February 2021}}).

==== Ecosystem of stagnant water ====
[[File:Danube Flower.jpg|thumb|''[[Nymphaea alba]]'' in the Danube Delta]]
This environment includes the lakes, and various ponds, streamlets and channels. It is characterized by a rich floating and submerse flora (''[[Myriophyllum]]'', ''[[Ceratophyllum]]'', ''[[Vallisneria]]'', under the water; ''[[Nymphaea alba]]'', ''[[Nuphar lutea]]'', ''[[Trapa natans]]'', ''[[Alisma plantago]]'', floating plants with roots near the lakes' borders; and ''[[Salvinia natans]]'', ''[[Stratiotes aloides]]'', ''[[Spirogyra]]'', floating plants without roots, having negative effect for aquatic [[bioproductivity]]). Of the fish, the most important are [[Tench]] (''Tinca tinca''), [[common bream]] (''Abramis brama''), [[common rudd]] (''Scardinius erythropthalmus''), [[Prussian carp]] (''Carassius auratus gibelio''), [[wels catfish]] (''Silurus glanis''), [[European perch]] (''Perca fluviatilis''), and [[northern pike]] (''Esox lucius'').

==== Ecosystem of marshy and flooding areas ====
[[File:Pelicani din Delta Dunarii.PNG|thumb|Pelicans in Danube Delta]]
[[File:RO004MS-04.jpg|thumb|The Danube Delta birds: [[grey heron]] (''Ardea cinerea''), [[mallard]] or wild duck (''Anas platyrhynchos''), [[great white pelican]] (''Pelecanus onocrotalus''), [[great crested grebe]] (''Podiceps cristatus''). Stamp of Romania, 2004]]

Reed plants and floating reed islands (called '''plaur''' in [[Romania]]) are the most common and well-known components of the Danube Delta. Vegetation of this ecosystem consists of the common reed (''[[Phragmites communis]]'') and, on near river banks, mace reed/cattail (''[[Typha latifolia]]'', ''[[Typha angustifolia]]''), sedge (''[[Carex dioica]]'', ''[[Carex stricta]]''), Dutch rush (''[[Scirpus radicans]]'', ''[[Schoenoplectus lacustris]]''), and brook mint (''[[Mentha aquatica]]''). They provide ideal spawning and nesting grounds. The '''plaur''' are a mixture of reed roots, grass and soil, usually floating or anchored to the riverbed. As a rule, the reed surrounds the lakes and ponds, and slowly invades the water surface.

This type of ecosystem is noted for its variety and large population of birds, some of them are very rare. The most important are the [[tufted duck]] (''Aythya fuligula''), [[red-crested pochard]] (''Netta rufina''), [[mallard]] (''Anas platyrhynchos''), [[greylag goose]] (''Anser anser''), [[pygmy cormorant]] (''Microcarbo pygmeus''), [[purple heron]] (''Ardea purpurea''), [[great egret|great white egret]] (''Egretta alba''), [[little egret]] (''Egretta garzetta''), [[Eurasian spoonbill]](''Platalea leucorodia''), [[great white pelican]] (''Pelecanus onocrotalus''), [[Dalmatian pelican]] (''Pelecanus crispus''), [[mute swan]] (''Cygnus olor''), and [[glossy ibis]] (''Plegadis falcinellus''). A recent and welcomed newcomer is the [[common pheasant|pheasant]] (''Phasianus colchicus'').

Among the mammals, there is the [[Eurasian otter]] (''Lutra lutra''), [[European mink]] (''Mustela lutreola''), [[stoat|little ermine]] (''Mustela erminea aestiva''), [[wild boar]] (''Sus scrofa''), and [[wildcat|wild cat]] (''Felis silvestris''), in winter the [[European hare]] (''Lepus europaeus'') and, on the brink of disappearing from the delta, the wolf and the fox. During the Middle Ages, the [[Caspian tiger]] (''Panthera tigris tigris'') was a resident across the steppes of Ukraine, including Danube Delta, and once, they were hunted to extinction and they're extirpated. The [[raccoon dog|East Asian raccoon dog]] (''Nyctereutes procyonoides''), bizam/introduced [[muskrat]] (''Ondatra zibethica''), and to some extent South American [[nutria]] (''Myocastor coypus''), are recent species that have successfully adapted.

==== River bank and levee ecosystems ====
[[File:Nycticorax nycticorax' AM1 slepowron.jpg|thumb|Black-crowned night heron]]

The firm land of the delta used to be covered with large groves of willow trees, which have been cut down almost entirely and replaced with Canadian poplars. On the river banks kept in their natural state, small groves of willow trees (''[[Salix alba]]'', ''[[Salix euxina|Salix fragilis]]'', ''[[Salix purpurea]]'', ''[[Salix pentandra]]'', and ''[[Salix triandra]]'') can still be found, mixed with white poplar (''[[Populus alba]]''). Occasionally, the willow trees form corridors along the arms and bigger channels of the Danube. On the [[levees]] of [[Letea]] and [[Caraorman]], mixed forests of oaks (''[[Quercus robur]]'', and ''[[Quercus pedunculiflora]]'') with various other  trees (''[[Fraxinus pallisiae]]'', ''[[Ulmus foliaceae]]'', ''[[Populus tremula]]''), shrubs (''[[Prunus spinosa]]'', ''[[Crataegus monogyna]]'', ''[[Rosa canina]]'', and ''[[Berberis vulgaris]]'', among others), and vines (''[[Vitis sylvestris]]'', ''[[Hedera helix]]'', ''[[Humulus lupulus]]'', ''[[Periploca graeca]]'', which reaches up to 25m) grow on [[sand dune]] areas. On the Letea levee, these exotic-looking forests grow especially in the depressions between the sand dunes, in small groves called '''hasmace'''. Fauna of this region include the [[meadow viper]] (''Vipera ursinii''), [[osprey]] (''Pandion haliaetus''), and [[Eurasian eagle owl]] (''Bubo bubo'').